Front consumables for pulse gmaw torches

ABSTRACT

A contact tip for a welding torch in accordance with the present invention includes an elongated, generally cylindrical body having a front contact end and an opposite rear retaining end. A central aperture is defined by an inner wall of the body. The aperture extends through the body from an opening at the rear retaining end to an opening at the front contact end. The aperture has a front portion and a wider diameter portion adjacent the front portion. The front portion generally has a length that is shorter than a length of the wider diameter portion. A consumable electrode wire fed through the aperture contacts the inner wall in the front portion but does not contact the inner wall in the wider diameter portion.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of U.S. Provisional Application No.61/186,257 filed Jun. 11, 2009.

TECHNICAL FIELD

This invention relates to front components of a GMAW (gas metal arcwelding), MIG (metal inert gas), MAG (metal active gas), SAW (submergedarc welding), or FCAW (flux cored arc welding) welding torch, and moreparticularly to contact tips and retaining heads of welding torches.

BACKGROUND OF THE INVENTION

A conventional welding torch generally includes a cable assemblyconnected to a torch body, a gooseneck extending from the body, and atorch head at a distal end of the gooseneck. The torch head typicallyincludes a retaining head and/or diffuser, a contact tip, and a nozzle.Welding wire (consumable electrode) and shielding gas are fed throughthe cable assembly and gooseneck to the torch head, where the weldingwire and shielding gas are fed out of the contact tip and nozzle.

Common metal welding techniques employ heat generated by electricalarcing to transition a portion of a workpiece to a molten state, and theaddition of filler metal from the welding wire.

Energy (e.g., welding current) is transferred from the cable assemblyand gooseneck through the front components of the torch including theretaining head and contact tip, to the consumable electrode weldingwire. When a trigger on the welding torch is operated or an “on” signalis assigned by a robot/automatic controller, electrode wire is advancedtoward the contact tip, at which point current is conducted from thecontact tip into the exiting welding wire. A current arc forms betweenthe electrode wire and the workpiece, completing a circuit andgenerating sufficient heat to melt the electrode wire to weld theworkpiece. The shielding gas helps generate the arc and protects theweld. As the electrode wire is consumed and becomes a part of the weld,new electrode wire is advanced, continuously replacing the consumedelectrode wire and maintaining the welding arc.

In order to increase welding speeds (e.g., the travelling speed) and toreduce spatter generation in welding applications, welding power sourceshave been utilizing modern waveforms that are represented by pulse andcontrolled short circuit. As shown in FIG. 1, these waveforms typicallyuse high peak current (I_Peak) in a short pulse period and high currentramp rate. For example, 300 amps is usually regarded as a high current(I_CV) for 1.13 mm (0.045 inch) outer diameter (OD) solid steelelectrode wire in constant voltage welding applications. In contrast, inpulse welding applications it is common for this same electrode wire tobe welded at a peak current of 500 amps. This 67% higher current resultsin 178% more heat generation (in joules) at the contact tip—electrodewire interface, according to the rule E=I²Rt where E represents heat injoules, I represents the current, R represents the electric resistanceacross the contact tip—electrode wire interface, and t represents aduration of time.

The high welding current and high current ramp rate transferring acrossthe contact tip—electrode wire interface during pulse weldingapplications causes local melt or evaporation (e.g., arc erosion) onboth the electrode wire and the contact tip. For example, burn marksform on the electrode wire as it is fed through the contact tip. Thispattern of burn marks on the electrode wire is a characteristic featureof modern pulse waveform welding and is not seen on electrode wire fedthrough contact tips during constant voltage welding modes. It is alsopostulated that similar damage occurs on the inner surface of thecontact tip where welding current is transferred to the electrode wire.However, burn marks cannot be or are difficult to observe on the innersurface of a used contact tip due to tribological wear of the burnfeatures by the feeding of the electrode wire against the inner surfaceof the contact tip.

Arc erosion during pulse welding applications causes substantial wearremoval of the contact tip, and practical data indicates that contacttips deteriorate faster in pulse welding applications in comparison toconstant voltage applications. For example, the length of a wear mark onan inner surface of a contact tip used for 20 minutes in a constantvoltage application was measured at approximately 3 mm. Using the samepack of electrode wire and the same wire feeding speed, the length of awear mark of a contact tip used for minutes in a pulse application wasmeasured at approximately 11 mm. After two hours of pulse welding, thewear mark on the same contact tip measured 17.5 mm. Thus, it is apparentthat pulse welding can cause significantly more contact tip wear thanconstant voltage welding.

As a contact tip is used and deteriorated, the energy transferefficiency between the contact tip and the electrode wire decreases.This results in lower energy consumption at the arc. When the energyconsumption is too low to maintain a smooth welding arc, stubbingoccurs, which causes undesired welding defects such as cold welding anddiscontinuous beads.

Further, electrode wire always has an inherent cast, or curvature, dueto the packaging of the electrode wire and the fact that the electrodewire if fed through a curved welding torch. The curved electrode wire isbent (elastically or plastically) inside the contact tip when it isforced into the central hole that extends through the contact tip. Theelectrode wire is typically bent against one “side” of the contact tiphole at a front end (called the front contact point) of the contact tipand at an opposite “side” of the contact tip hole at a rear end (calledthe rear contact point) of the contact tip. This mechanical bend isessential for the contacting force and ensures electrical conductionbetween the electrode wire and the contact tip.

FIG. 2 illustrates the contour of a section of electrode wire 20 insidea used (worn) contact tip 22. As the contact tip 22 is used and worn,the front portion 24 of the contact tip hole is damaged (e.g., keyholedwhen viewed from the front end), and the contact point 26 becomes acontact area 28. The welding current, which in a new contact tip isdelivered to the electrode wire at the very front end of the bore 24, isnow transferred across the contact area 28 (as depicted by arrow 30).This increases the total electric resistance of the welding circuit andcauses low welding current, or low efficiency of the contact tip.

One method that has been used to mitigate the deterioration of thecontact tip is to increase the mechanical contact force between thecontact tip and the electrode wire, such as by spring mechanisms,S-shaped contour of the bore of the contact tip, or introduction of morecurvature to the electrode wire before feeding it into the contact tip.Improving the contact force reduces the electrical resistance and thefluctuation of electrical resistance across the interface, thusimproving the contact tip efficiency. However, these designs are eithertoo expensive to be commercialized, or too fragile to tolerate the harshnature of the welding environment, such as high temperatures andspatter.

SUMMARY OF THE INVENTION

The present invention provides a welding torch retaining head andcontact tip that maintains and/or increases the mechanical contact forceof electrode wire against the contact tip, thereby reducing electricalresistance and arc erosion. In contrast to the prior art which increasescontact force of the electrode wire against the contact tip, the presentinvention reduces the size of the contact area. As shown in FIG. 2,though the electrode wire contacts the contact tip 22 across the entirecontact area 28 in a conventional worn contact tip, the welding current(depicted by arrow 30) tends to travel across the interface at a frontregion 32 due to the electrical resistance of the contact tip 22(typically made out of copper or copper alloys) being lower than that ofthe electrode wire 20 (typically made out of steel, stainless steel, oraluminum). The mechanical support provided by a rear region 34 of thecontact area 28 does not contribute to the efficiency of the contacttip. A contact tip in accordance with the present invention has aninternal portion removed that corresponds to a rear region of the frontcontact area that would provide mechanical support but not the weldingcurrent to the electrode wire. Removing this mechanical support securesthe contact force at the front region. Thus, the contact force betweenthe contact tip and the electrode wire is wholly applied at a frontregion of the contact area where electrical current travels. Theresulting improved mechanical contact between the contact tip andelectrode wire reduces electrical resistance and consequently reducesarc erosion. This improves the stability of electrical conduction, thewelding current, the welding arc, and the performance of the contacttip. Removal of an internal portion of the contact tip also reduces oreliminates fluctuations in the mechanical support provided to theelectrode wire as the electrode wire is fed through the contact tip atspeeds of 13 to 42 cm/second (300 to 1000 inches per minute), thusreducing fluctuations of the welding arc and arc erosion on the contacttip.

More particularly, a contact tip for a welding torch in accordance withthe present invention includes an elongated, generally cylindrical bodyhaving a front contact end and an opposite rear retaining end. A centralaperture is defined by an inner wall of the body. The aperture extendsthrough the body from an opening at the rear end to an opening at thefront end. The aperture has a front portion and a wider diameter portionadjacent the front portion. The front portion generally has a lengththat is shorter than a length of the wider diameter portion. Aconsumable electrode wire fed through the aperture does not contact theinner wall in the wider diameter portion.

The aperture may have a generally stepped cross-sectional shape along anaxial direction. The aperture may have three coaxial portions includingthe front portion, a middle portion defining the wider diameter portion,and a rear portion. The front, middle, and rear portions each have adiameter defined by the inner wall of the body. The diameter of themiddle portion is larger than the diameters of each of the front andrear portions. A consumable electrode wire fed through the aperture onlycontacts the inner wall in the front and rear portions. The diameter ofthe front portion may be generally 2% to 10% greater than a diameter ofthe consumable electrode wire that is fed through the hole. The diameterof the rear portion may be generally 5% to 15% greater than the diameterof the consumable electrode wire. The diameter of the middle portion maybe at least generally 0.15 mm larger than the diameter of the frontportion, and the diameter of the wider diameter portion may be variable.The length of the front portion may be generally between 1.5 mm and 15mm, the length of the rear portion may be generally between 1.5 mm and15 mm, and the length of the middle portion may be greater than thelength of the front portion and the rear portion.

Alternatively, the contact tip may include a rear insert inserted intothe opening at the rear end of the body. The rear insert includes acentral bore extending therethrough. The bore of the rear insert isgenerally continuous with the aperture in the contact tip body. Thediameter of the middle portion is generally larger than the diameter ofthe front portion and the diameter of the bore of the rear insert.

The contact tip may include a front insert inserted into the opening atthe front end of the body. The front insert includes a central boreextending therethrough. The bore in the front insert is generallycontinuous with the aperture in the body and has a length that isshorter than the length of the middle portion. The diameter of themiddle portion is generally larger than the diameter of the rear portionand a diameter of the bore in the front insert.

Optionally, the contact tip body may be formed of two interlockingmembers.

The contact tip may be arranged in combination with a retaining head fora welding torch. The retaining head has a front end, a rear end, and anopening at the front end. The contact tip is retained in the opening atthe front end of the retaining head. The contact tip and the retaininghead together define a passageway for the consumable electrode wire. Thepassageway includes the front portion of the contact tip aperture, arear portion disposed in the retaining head, and a middle portion atleast partially defined by the wider diameter portion of the contact tipaperture. The front portion of the passageway may have a length that isshorter than a length of the middle portion. A consumable electrode wirefed through the passageway does not contact the retaining head andcontact tip in the middle portion of the passageway and only contactsthe retaining head and the contact tip in the front and rear portions ofthe passageway.

Optionally, the length of the front portion may be generally between 1.5mm and 15 mm. The middle portion may be defined by the wider diameterportion of the contact tip aperture and the opening in the retaininghead. A rear insert may be inserted into the retaining head. The rearinsert may include a central bore extending therethrough. The bore mayform a portion of the passageway and may be generally continuous withthe middle portion of the passageway. A front insert may be insertedinto the opening at the rear end of the contact tip body. The frontinsert may include a central bore extending therethrough. The bore ofthe front insert may partially define the front portion of thepassageway and may be generally continuous with the middle portion ofthe passageway.

A welding torch assembly in accordance with the present inventionincludes a retaining head and a contact tip engaged with the retaininghead. The retaining head and the contact tip together define apassageway for a consumable electrode wire. The passageway includes afront portion, a rear portion, and a middle portion between the frontand rear portions. The middle portion has a diameter and a length thatis larger than a length and a width of the front and rear portions. Aconsumable electrode wire fed through the passageway does not contactthe retaining head and contact tip in the middle portion of thepassageway and only contacts the retaining head and the contact tip inthe front and rear portions of the passageway.

Optionally, the length of the front portion may be generally between 1.5mm and 15 mm. The middle portion of the passageway may be formed by oneof the contact tip alone or the contact tip and the retaining headtogether. A rear insert may be inserted into the retaining head. Therear insert includes a central bore extending therethrough. The bore inthe rear insert at least partially forms the rear portion of thepassageway and is generally continuous with the middle portion of thepassageway. A front insert may be inserted into the contact tip. Thefront insert includes a central bore extending therethrough. The bore inthe front insert at least partially forms the front portion of thepassageway and is generally continuous with the middle portion of thepassageway.

These and other features and advantages of the invention will be morefully understood from the following detailed description of theinvention taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a graph of welding current versus time illustrating a constantvoltage waveform and a pulse welding waveform;

FIG. 2 is a schematic sectional view of a worn conventional contact tipillustrating the contour of electrode wire inside the contact tip andthe contact of the electrode wire against the contact tip;

FIG. 3 is a perspective view of a robotic GMAW torch including a contacttip and retaining head in accordance with the present invention;

FIG. 4 is a sectional view of a contact tip in accordance with thepresent invention;

FIG. 5 is a sectional view of a contact tip and retaining head assemblyin accordance with the present invention;

FIG. 6 is a sectional view of a contact tip and retaining head assemblyin accordance with the present invention;

FIG. 7 is a sectional view of a contact tip and retaining head assemblyin accordance with the present invention;

FIG. 8 is a sectional view of a contact tip and retaining head assemblyin accordance with the present invention;

FIG. 9 is a sectional view of a contact tip and retaining head assemblyin accordance with the present invention; and

FIG. 10 is a sectional view of a contact tip and retaining head assemblyin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in detail, numeral 110 generally indicatesa welding torch such as a gas metal arc welding (GMAW) torch or asimilar welding torch. As shown in FIG. 3, the welding torch 110 broadlyincludes a torch body 112, a gooseneck 114 extending from a forward endof the torch body, and a contact tip assembly 116 at a distal end of thegooseneck. The contact tip assembly 116 generally includes frontconsumable components such as a retaining head and contact tip which arediscussed in greater detail below. During use of the welding torch 110,the contact tip assembly 116 may be covered and protected by a nozzle. Acable (not shown) is connected to a rear end of the torch body 112. Thecable supplies at least one of electrical current, shielding gas, and aconsumable electrode wire (e.g., a metal welding wire) to the torch body112. The electrical current, shielding gas, and consumable electrodewire travel through the torch body 112 to the gooseneck 114 andultimately exit through an orifice in the contact tip assembly 116.

The welding wire, when energized for welding, carries a certainelectrical potential. When the welding wire approaches or makes contactwith target metal workpieces, an electrical arc is generated, and anelectrical circuit is completed and current flows through the weldingwire, across the metal workpieces and to ground. The current causes thewelding wire and the parent metal of the workpieces in contact with thewelding arc to melt, thereby joining the workpieces as the meltsolidifies.

Turning to FIG. 4, a contact tip 120 in accordance with the inventionhas an elongated, generally cylindrical body 122 that may be made ofcopper, a copper alloy, or other similarly suitable material. The body122 has a front contact end 124 having an opening from which electrodewire exits and an opposite rear retaining end 126 having an opening intowhich the electrode wire is fed. A central aperture 128 defined by aninner wall of the body extends through the body from the opening at therear end 126 to the opening at the front end 124. The central aperture128 provides a passageway for electrode wire through the contact tip120, and has a generally stepped cross-sectional shape along an axialdirection of the contact tip. More specifically, the central aperture128 has a front portion 130 and a wider diameter portion 132 adjacentthe front portion. The wider diameter portion 132 generally has a largerdiameter than the front portion 130. The front portion 130 generally hasa length that is shorter than the length of the wider diameter portion132. Due to the short length of the front portion 130 and the wideningof the passageway through the contact tip 120 in the adjacent widerdiameter portion 132, a consumable electrode wire 134 fed through thecentral aperture 128 does not contact the inner wall of the contact tipbody 122 in the wider diameter portion. Thus, the wider diameter portion132 does not provide any mechanical support for the electrode wire 134,and the contact force between the contact tip 120 and the electrode wireis applied in the front portion 130 where electric current istransferred from the contact tip to the electrode wire. The improvedelectrical contact between the contact tip and electrode wire reduceselectrical resistance, which reduces arc erosion and lengthens theeffective life of the contact tip.

In one embodiment, the contact tip aperture 128 may have three coaxialportions including the front portion 130 at the front end 124 of thecontact tip, a rear portion 136 at the rear end of the contact tip, andthe wider diameter portion 132 which is a middle portion disposedbetween the front and rear portions. The diameter of the middle portion132 is larger than the diameter of both the front portion 130 and therear portion 136, and the electrode wire 134 only contacts the innerwall in the front and rear portions of the aperture 128 and does notcontact the inner wall in the middle portion 132. The diameter of thefront portion 130 may be generally 2 to 10 percent greater than thediameter of the electrode wire 134 that is fed through the aperture 128(e.g., the electrode wire may have a diameter of approximately 0.045inches). The diameter of the rear portion 136 may be generally 5 to 15percent greater than the diameter of the electrode wire 134. Thediameter of the middle portion 132 may be at least generally 0.15 mmlarger than the diameter of the front portion 130. The length of thefront portion 130 may be generally between 1.5 and 15 mm, and forexample may be 8 mm. The length of the rear portion 136 may be generallybetween 1.5 and 15 mm, and for example may be 10 mm. The length of themiddle portion 132 is greater than the length of either the frontportion 130 or the rear portion 136.

The diameter of the wider, middle portion 132 may be variable orirregular. For example, instead of having a single, generally constantdiameter throughout, the middle portion 132 may have a diameter thatvaries stepwise in an axial direction or may have a sloped or slottedprofile. As shown in FIG. 4, the diameter of the middle portion 132decreases from its largest value down to the diameter of the frontportion 130 at the boundary between the front portion and the middleportion. The inner wall of the contact tip body 122 thereby has a coneshape at the transition from the middle portion 132 to the front portion130. The middle portion 132 of the aperture 128 need not have anyspecific cross-sectional shape so long as the diameter of the middleportion 132 is generally large enough to form an open space in thecontact tip body 122 in which an electrode wire travelling through theaperture will not contact the contact tip body. Also, the rear portion136 of the contact tip aperture 128 may have a slopped rear end 137 thatforms a cone or other similar shape. The slopped rear end 137 may aidein feeding an electrode wire into the contact tip aperture 128.

The contact tip 120 may include a cooperable mounting feature 138 suchas threads that cooperate with a related feature in a retaining head formounting and securing the contact tip in the retaining head. Alternativemeans for mounting the contact tip in a retaining head include but arenot limited to solders, crimps, forges, and press fit connections.

For example, turning to FIG. 5, a welding torch assembly of frontcomponents in accordance with the invention includes a contact tip 220mounted and secured in a retaining head 240. The retaining head 240 hasa front end 242, an opposite rear end 244, and an opening 246 at thefront end. The opening 246 may generally extend from the front end 242to the rear end 244 to form an aperture through the retaining head. Thecontact tip 220 is securely retained in the opening 246 at the front endof the retaining head. The opening 246 in the retaining head iscontinuous with the central aperture 228 through the contact tip body,and the contact tip 220 and retaining head 240 together define apassageway for a consumable electrode wire.

Optionally, as shown in FIG. 5, the contact tip body may be formed oftwo interlocking members 248, 250 for ease of manufacturing. The frontportion 230 of the central aperture 228 is formed in the first member248, the rear portion 236 of the aperture is formed in the second member250, and the middle portion 232 is formed partially in the first memberand partially in the second member. However, the middle portion may beformed mostly or entirely in either the first member or the secondmember.

Turning to FIG. 6, the contact tip 320 may optionally include a rearinsert 352 that is inserted into the rear portion 336 of the centralaperture 328 through the opening at the rear end 326 of the contact tip.The rear insert 352 includes a central bore 354 extending through therear insert. The central bore 354 is generally continuous with thecentral aperture 328 in the contact tip body 322, and generally definesthe small diameter rear portion of the passageway through the contacttip 320 such that the diameter of the middle portion 332 of the aperture328 is generally larger than the diameter of the front portion 330 ofthe aperture and larger than the diameter of the bore 354 in the rearinsert.

Turning to FIG. 7, the contact tip 420 may optionally include a frontinsert 456 that is inserted into the front portion 430 of the centralaperture 428 through the opening at the front end 424 of the contacttip. The front insert 456 includes a central bore 458 extending throughthe front insert. The central bore 458 is generally continuous with thecentral aperture 428 in the contact tip body 422, and generally definesthe small diameter front portion of the passageway through the contacttip 420 such that the diameter of the middle portion 432 of the aperture428 is generally larger than the diameter of the rear portion 436 of theaperture 428 and larger than the diameter of the bore 458 in the rearinsert.

The rear insert 352 and front insert 456 may be made of a material thatis the different than the material of construction of the contact tipbody. For example, the rear insert and front insert each may be made ofcopper, a copper alloy such as a precipitation hardened copper alloy ora mechanical alloyed copper alloy, a copper matrix composite, or asimilarly suitable material.

With reference to FIG. 8, as mentioned above, the contact tip 520 andretaining head 540 may together form an assembly and may define apassageway through the assembly for a consumable electrode wire. Forexample, the passageway may include the front portion 530 of the contacttip aperture 528, a rear portion 560 disposed in the retaining head 540,and a middle portion 562 at least partially defined by the widerdiameter portion 532 of the contact tip aperture 528. In the embodimentshown in FIG. 8, the middle portion 562 is entirely defined by the widerdiameter portion 532 of the contact tip aperture 528. The middle portion562 formed in the contact tip body 522 is continuous with and adjacentto the rear portion 562 formed in the retaining head 540. The frontportion 530 of the passageway has a length that is shorter than thelength of the middle portion 562. For example, the length of the frontportion 530 may be generally between 1.5 and 15 mm. A consumableelectrode wire fed through the passageway does not contact the retaininghead 540 and contact tip 520 in the middle portion 562 of the passagewayand only contacts the retaining head and contact tip in the frontportion 530 and rear portion 560 of the passageway.

Optionally, as shown in FIG. 9, the middle portion 662 may be formed inboth the contact tip 620 and retaining head 640. The middle portion 662may have a variable diameter, as long as the middle portion is wider indiameter than the front portion 630 and rear portion 660 of thepassageway, and an electrode wire does not touch any part of the wall ofthe middle portion 662 when fed through the assembly of the retaininghead 640 and the contact tip 620.

Also, a rear insert 664 may be inserted into the retaining head 640. Therear insert 664 may be made of a copper alloy, a high hardness toolsteel, cast iron, ceramics, PTFE, a PTFE containing polymer, or asimilarly suitable material. The rear insert 664 includes a central bore666 extending therethrough which forms a portion of the passageway andis generally continuous with the middle portion 662 of the passageway.The bore 666 through the rear insert 664 has a diameter that isgenerally smaller than the diameter of the middle portion 662 of thepassageway. However, the bore 666 may include a slopped increaseddiameter portion 668 that forms a cone or other similar shape whichaides in feeding an electrode wire into the rear insert 664.

Turning to FIG. 10, the contact tip 720 may include a front insert 770that is inserted into the central aperture 728 of the contact tipthrough the opening at the rear end 726. The front insert 770 includes acentral bore 772 extending therethrough which partially defines thefront portion 774 of the passageway. The remainder of the front portion774 of the passageway is defined by the front portion 730 of the contacttip aperture 728. The central bore 772 of the front insert generally hasa diameter that is smaller than the diameter of the middle portion 762and is generally equal to or slightly smaller than the diameter of thefront portion 730 of the contact tip aperture 728. However, the bore 772may include a slopped increased diameter portion 776 that forms a coneor other similar shape which aides in feeding an electrode wire into thefront insert 770.

Although the invention has been described by reference to specificembodiments, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but that it have the full scope defined by thelanguage of the following claims.

1. A contact tip for a welding torch, the contact tip comprising: anelongated, generally cylindrical body having a front contact end and anopposite rear retaining end; and a central aperture defined by an innerwall of said body, said aperture extending through said body from anopening at said rear end to an opening at said front end; said aperturehaving a front portion and a wider diameter elongated portion adjacentsaid front portion, said front portion generally having a length that isshorter than a length of said wider diameter portion; wherein aconsumable electrode wire fed through said aperture does not contactsaid inner wall in said wider diameter portion.
 2. The contact tip ofclaim 1, wherein said aperture has a generally stepped cross-sectionalshape along an axial direction.
 3. The contact tip of claim 1, wherein:said aperture has three coaxial portions including said front portion, amiddle portion defining said wider diameter portion, and a rear portion;said front, middle, and rear portions each having a diameter defined bysaid inner wall of said body; the diameter of said middle portion beinglarger than the diameters of each of said front and rear portions; andsaid consumable electrode wire fed through said aperture only contactssaid inner wall in said front and rear portions.
 4. The contact tip ofclaim 3, wherein: the diameter of said front portion is generally 2% to10% greater than a diameter of said consumable electrode wire that isfed through said aperture; the diameter of said rear portion isgenerally 5% to 15% greater than the diameter of said consumableelectrode wire; and the diameter of said middle portion is at leastgenerally 0.15 mm larger than the diameter of said front portion.
 5. Thecontact tip of claim 3, wherein: the length of said front portion isgenerally between 1.5 mm and 15 mm; a length of said rear portion isgenerally between 1.5 mm and 15 mm; and the length of said middleportion is greater than the length of said front portion and said rearportion.
 6. The contact tip of claim 1, wherein the diameter of saidwider diameter portion is variable.
 7. The contact tip of claim 1,wherein: said aperture has a middle portion defining said wider diameterportion, and a rear portion; said middle portion is disposed betweensaid front and rear portions; said contact tip includes a rear insertinserted into said opening at the rear end of said body, said rearinsert including a central bore extending therethrough, said bore beinggenerally continuous with said aperture of said body; and a diameter ofsaid middle portion is generally larger than a diameter of said frontportion and a diameter of said bore.
 8. The contact tip of claim 1,wherein: said aperture has a middle portion defining said wider diameterportion, and a rear portion; said middle portion is disposed betweensaid front and rear portions; said contact tip includes a front insertinserted into said opening at the front end of said body, said frontinsert including a central bore extending therethrough, said bore beinggenerally continuous with said aperture of said body; said bore having alength that is shorter than the length of said middle portion; and adiameter of said middle portion is generally larger than a diameter ofsaid rear portion and a diameter of said bore.
 9. The contact tip ofclaim 1, wherein said body is formed of two interlocking members. 10.The contact tip of claim 1 in combination with a retaining head for awelding torch, wherein: said retaining head has a front end, a rear end,and an opening at said front end; said contact tip being retained insaid opening at said front end of said retaining head; said contact tipand said retaining head together define a passageway for said consumableelectrode wire; said passageway including said front portion of saidcontact tip aperture, a rear portion disposed in said retaining head,and a middle portion at least partially defined by said wider diameterportion of said contact tip aperture; said front portion of saidpassageway having a length that is shorter than a length of said middleportion; wherein a consumable electrode wire fed through said passagewaydoes not contact said retaining head and contact tip in said middleportion of said passageway and only contacts said retaining head andsaid contact tip in said front and rear portions of said passageway. 11.The combination of claim 10, wherein the length of said front portion isgenerally between 1.5 mm and 15 mm.
 12. The combination of claim 10,wherein said middle portion is defined by said wider diameter portion ofsaid contact tip aperture and said opening of said retaining head. 13.The combination of claim 10, including a rear insert inserted into saidretaining head, said rear insert including a central bore extendingtherethrough, said bore of said rear insert forming a portion of saidpassageway and being generally continuous with said middle portion ofsaid passageway.
 14. The combination of claim 10, including a frontinsert inserted into said opening at said rear end of said contact tipbody, said front insert including a central bore extending therethrough,said bore of said front insert partially defining said front portion ofsaid passageway and being generally continuous with said middle portionof said passageway.
 15. A welding torch assembly comprising: a retaininghead; and a contact tip engaged with said retaining head; said retaininghead and said contact tip together defining a passageway for aconsumable electrode wire; said passageway including a front portion, arear portion, and a middle portion between said front and rear portions;said middle portion having a diameter and a length that is larger than alength and a width of said front and rear portions; wherein a consumableelectrode wire fed through said passageway does not contact saidretaining head and contact tip in said middle portion of said passagewayand only contacts said retaining head and said contact tip in said frontand rear portions of said passageway.
 16. The welding torch assembly ofclaim 15, wherein the length of said front portion is generally between1.5 mm and 15 mm.
 17. The welding torch assembly of claim 15, whereinsaid middle portion of said passageway is formed by one of said contacttip alone and said contact tip and said retaining head together.
 18. Thewelding torch assembly of claim 15, including a rear insert insertedinto said retaining head, said rear insert including a central boreextending therethrough, said bore of said rear insert at least partiallyforming said rear portion of said passageway and being generallycontinuous with said middle portion of said passageway.
 19. The weldingtorch assembly of claim 15, including a front insert inserted into saidcontact tip, said front insert including a central bore extendingtherethrough, said bore of said front insert at least partially formingsaid front portion of said passageway and being generally continuouswith said middle portion of said passageway.